Really a good game, I very much enjoyed the first one. However, this one felt like it could use some changes in a few areas.
1. The movement speed seemed very... slow. High graphics, low graphics didn't seem to make a difference. It just seemed quite slow to me.
2. The hints, not all that helpful, the instructions for the keys were more useful than the hints, which didn't seem to add much to the game. And the one point in the game where I could have used a hint there was none (needed reminding that you shoot the force fields to disable them). That being said I don't think hints in this case should correspond to a different difficulty, just weather or not you want the annoying hints on. That is my thought.
3. I think the color change with regards to resistance (for sunlight or water) although ok, isn't all that great, I would rather have a timer.
4. There are places where you can get stuck, it would be better to have a suicide button so we don't have to quit and reload.
Also in the medals you mention the 'first' light upgrade. I did not notice any others I wonder if there is more than one? If so how many are there, I am surprised there isn't a medal for getting all light upgrades.
I also wonder if there is more than one ending. i didn't see another way out (as you can't jump up through holes). Yet the game ends in a rather ambiguous way. But I don't see any other way to end it. If there is I would love to play for it, again based on the medals I rather think there may not be.
Again though I did really enjoy the game, as well as the music (which was really very good and something I usually don't compliment on). It could use some tweaks because the movement thing really wears thin quickly. Overall though pretty sweet game definitely worth one play through. 4/5 8/10. Keep up the good work, I look forward to what comes next.